Some SPC Watch Statistics

The numbers below are for 20 years of watches (1980-1999).
Watches with no reports are included in the averages and
probabilities.
First, all reports:

WATCH TYPE
TOR SVR
Average # of tornadoes: 2.2 0.5
Average # of wind: 7.1 6.0
Average # of hail reps: 6.3 3.8
TOR SVR
Probability of 1 or more tornadoes: 56.1 22.7
Probability of 1 or more wind events: 75.5 72.5
Probability of 1 or mail hail reps: 67.0 62.1
Probability of 5 or more tornadoes: 15.1 1.8
Probability of 10 or more wind: 22.9 19.1
Probability of 10 or more hail reps: 22.4 11.7

Conclusion: Tornadoes are much more likely in tornado
watches than severe thunderstorm watches.

Next -- same thing but for significant reports (2" or
larger hail, 65 kt or greater wind speed reported, and F2 or stronger
tornadoes):

TOR SVR
Average # of tornadoes: 0.5 0.1
Average # of wind: 0.4 0.3
Average # of hail: 0.7 0.3
TOR SVR
Probability of 1 or more tornadoes: 21.2 4.8
Probability of 1 or more wind: 19.5 15.5
Probability of 1 or more hail: 25.0 13.9
Probability of 5 or more tornadoes: 2.5 0.2
Probability of 10 or more wind: 0.5 0.3
Probability of 10 or more hail: 0.7 0.1

In summary: tornado probabilities are much higher in tornado watches than
severe thunderstorm watches, as are the probabilities of any type of
significant severe report (most notably tornadoes and large hail).